In drilling operations, it is common practice to removed thousands of feet of pipe from a well hole in order to replace a worn drill bit. The pipe is uncoupled and stacked as it is removed. In order to reduce the time for accomplishing the repetitive task of uncoupling and storing pipe, automation of various steps involved in the uncoupling process has resulted. Remotely controlled racking arms have been devised for gripping portions of pipes. A power torque winch has come into use for breaking the tight connection between two adjacent sections of pipe rather than applying mechanical wrenches requiring a number of workmen to do the same job. A power spinning wrench has recently come into use for rapidly rotating the pipe to be removed with respect to the drill string so that the pipe can be uncoupled and moved to temporary storage. Finger board sections have been employed on the derrick to receive upper portions of pipe stands to permit vertical storing of the pipe stands. In addition, a computerized system has been proposed which monitors the position of racker arms for grabbing pipes and controls the movement of the racker arms.
Although the foregoing contributions to the task of uncoupling, as well as coupling, pipe stands have improved the efficiency of the drilling operation, some significant deficiencies still remain. None of the prior art systems is fully automated since verification of each step of the system operation is not automatically done before a next step is initiated. In this regard, the present invention utilizes sensing means, such as transducers, for use in indicating to a programmable controller whether a pipe stand has actually been grasped by a racking arm. There is no need for a drill rig operator to check whether this grasping step has occurred since the system itself can make such a determination. In addition, the present invention incorporates newly devised controllable arms and a transport assembly for grabbing and holding pipe stands during the uncoupling and coupling operations. These devices can be used with presently available drilling equipment and are adapted to be readily utilized with and supported by a conventional derrick or drill rig floor.